The present invention, in some embodiments thereof, relates to polymeric conjugates and their use in therapy and/or diagnosis and, more particularly, but not exclusively, to bone-targeted polymeric conjugates and to uses thereof in treating and/or monitoring bone-related diseases and disorders.
A limiting factor for the success of cancer chemotherapy lies in the accumulation of the therapeutic agents in tumors. Difficulties are encountered in the administration of sufficient quantities of chemotherapeutic agents which provide the in vivo concentration of the chemotherapeutic agent required to afford an effective killing of cancer cells.
The accumulation of chemotherapeutic agents in tumors depend on several factors including the size, surface characteristics and circulation half-life of the chemotherapeutic agents, as well as the degree of angiogenesis in the tumors.
Polymer-anticancer drug conjugates have been investigated, as therapies against cancer aimed at addressing the relevant limitations of current protocols using low molecular weight drugs. The coupling of anti-cancer agents with water-soluble polymers has been demonstrated to improve both the safety profile and antitumor efficacy due to, for example, possible avoidance of toxic formulations; and to contribute to improved biodistribution and pharmacokinetics, which results from their restricted distribution and the enhanced permeability and retention (EPR) effect, which promotes passive targeting to solid tumors.
An example of the increased activity yet reduced toxicity obtained by conjugation of anti-tumor drugs to water-soluble polymers is presented in U.S. Pat. No. 6,884,817.
Recent studies have been directed to either synthesizing targeted conjugates [Allen, T. M. Nat. Rev. Cancer 2002; 2: 750-763; Brumlik et al. Expert Opin. Drug Delivery 2008; 5: 87-103; Segal et al. PLoS ONE 2009; 4: e5233; Canal et al. J. Controlled Release 2010, 146: 388-399] or polymers bearing two anticancer drugs for combination therapy [Vicent et al. Angew. Chem., Int. Ed. Engl. 2005; 44 (26); 4061-4066; Pasut, et al. J. Med. Chem. 2009; 52; 6499-6502. Greco, F.; Vicent et al. J. Adv. Drug Delivery Rev. 2009; 61: 1203-1213.]. Satchi-Fainaro et al. disclose targeted conjugates, in which paclitaxel (PTX) and alendronate (ALN) are coupled to HPMA copolymer [Miller et al. Angew. Chem., Int. Ed. Engl. 2009; 48: 2949-2954.]. An exemplary such conjugate was shown to exhibit increased anticancer and anti-angiogenic activity with respect to the free drugs and, remarkably, reduced toxicity. Other studies in this regard are described in Segal et al. [PLoS ONE 2009; 4: e5233]; and Wang et al. [Mol. Pharmaceutics 2006; 3: 717-25].
WO 2004/062588 teaches water soluble polymeric conjugate for bone targeted drug delivery. The polymeric drug delivery systems taught in this application are based on hydroxypropyl methacrylate (HPMA) conjugates of bone-targeting agents, such as alendronate and D-Asp8, together with a chemotherapeutic agent (e.g., tetracycline).
WO 2009/141823 teaches polymeric conjugates comprising a plurality of polymeric backbones (e.g., derived from HPMA) having attached thereto a bone-targeting moiety such as alendronate and an anti-angiogenesis agent such as paclitaxel or TNP-470.
WO 2009/141826 teaches conjugates of a polymer (e.g., PGA) having attached thereto an angiogenesis targeting moiety and a therapeutically-active agent such as an anti-cancer agent or anti-angiogenesis agent.
WO 2009/141827 teaches conjugates of hydroxypropyl methacrylamide (HPMA)-derived copolymers having attached thereto anti-angiogenesis agents such as TNP-470 and a high load of a bone-targeting moiety such as alendronate (ALN).
PTX is a potent anticancer drug, used for the treatment of several cancers, however, it is associated with severe side effects due to both its scarce tumor selectivity and the formulation in Cremophor EL. In recent years, it has become evident that paclitaxel at low doses has antiangiogenic properties (Wang, et al. Anticancer Drugs 2003; 14: 13-19).
A HPMA copolymer conjugate of paclitaxel has been described by Meerum Terwogt et al. [PNU166945; Anticancer drugs 2001; 12: 315-323]. This conjugate was aimed at improving drug solubility and providing controlled release of paclitaxel.
Bisphosphonates, such as alendronate (ALN), are molecules used to treat osteoporosis, bone metastases and to prevent bone fractures. These compounds exhibit an exceptionally high affinity to the bone-mineral hydroxyapatite, and therefore are known to be used also as a targeting moiety [Uludag, H. Curr Pharm Des 2002; 8: 1929-1944].
Alendronate is considered potent for the treatment of bone related diseases and cancer-associated hypercalcemia. It was shown to have antitumor effect in several in vivo cancer models through several different mechanisms [Tuomela et al. 2008, BMC Cancer 8:81; Molinuevo et al. 2007, Eur J Pharmacol 562:28-33; Hashimoto et al. 2005, Cancer Res 65: 540-545]. In addition, alendronate was found to have anti-angiogenic activity through (i) suppression of VEGF-induced Rho activation in an ovarian cancer model [Hashimoto et al. 2007, Biochem Biphys Res Commun 354: 478-484], (ii) inhibition of farnesyl pyrophosphate synthase, in the mevalonate pathway [Russell R G 2007, Pediatrics 119 Suppl 2: S150-162]; and (iii) regulation of cellular level of MMP-2 expression in osteosarcoma cell lines [Cheng et al. 2004, Pediatr Blood Cancer 42; 410-415].
Poly(ethylene glycol) (PEG) is a polymer approved for human use. While it is known to be non-biodegradable, it is readily excretable after administration into living organisms. High excretion is typically observed for polymers having a molecular weight lower than 40 kDa or for polymers having a hydrodynamic diameter of less than 100 nm. In vitro studies showed that its presence in aqueous solutions has shown no deleterious effect on protein conformation or activities of enzymes. Covalent attachment of PEG to biologically active compounds is described, for example, in Yamaoka et al. [1994, J Pharm Sci 83; 601-606].
However, the potential of PEG as a carrier of low molecular weight drugs (small molecules) has been limited by its intrinsic low loading, owing to the polymer's chemical structure. In fact, only the end chain groups (at the termini) of PEG can be modified and exploited for drug coupling.
Wang et al. [in Bioconj. Chem., 2003, 14, 853-859] teach bone-targeted drug delivery systems based on water-soluble polymers such as PEG and HPMA, have attached thereto bone targeting moieties such as alendronate and Asp8, and FITC as a model drug for detection purposes.
Katsumi et al. [in J. Pharma. Sci., 2011, 100, 3783-3792] also teach PEG-conjugated alendronate, and its effect in treating osteoporosis.
Pasut et al. [in J. Bioactive and Comp. Polym., 2005, 20, 213] discloses PEG-epirubicin conjugates with high drug loading, having dendrimeric (dendritic) structures based on adipic acid or beta-glutamic acid branching units.
Pasut et al. [in J. Med. Chem. 2009; 52 (20), 6499-6502] reported on the synthesis, characterization, and biological performance of PEG conjugates carrying epirubicin (EPI) and one or more nitric oxide (NO) molecules per PEG.
Bioconjugates of poly(ethylene glycol), gemcitabine (an antitumor agent), and a targeting moiety, differing in the drug loading, have also been reported [Pasut et al, J. Control Release. 2008; 127(3): 239-48].
Canal et al. [in J. Controlled Release 2010; 146: 388-399] disclosed a series of PEG-epirubicin conjugates with different folic acid contents per polymeric chain. A dendron structure was synthesized at one end of the PEG chain with the aim of increasing the number of folic acid molecules.
Choe et al. [in J. Controlled Release 2002; 79: 41-53] reported on a study of various N-amino PEG-prodrugs of ara-C. In an LX-1 solid lung tumor model, some of the PEG prodrugs exhibited superior activity to ara-C when compared on a molar basis. However, the degree of loading ara-C onto PEG was limited by the high viscosity of the obtained solutions.
Choe et al. [in J. Controlled Release 2002; 79: 55-70] described the synthesis of branched PEG (40,000) acids which had been achieved using aspartic acid (Asp) and AspAsp dendrons. Conjugation of these dendritic acids with cytosine arabinoside (ara-C) was achieved by the use of spacers that allowed a greater separation of the branches to accommodate several large ara-C molecules in proximity to each other.
Berna et al. [in Biomacromolecules 2006, 7:146-153] synthesized novel monodisperse PEG-dendrons with amino or carboxylic terminal groups. The PEG-based dendrons were prepared using monodisperse Fmoc-amino PEG propionic acid as a monomer, and cadaverine, tris(2-aminoethyl)amine or lysine as the branching moieties.
Other combinations of dendritic structures and drugs, or other biologically active molecules, are disclosed, for example, in U.S. Pat. Nos. 5,714,166, 6,417,339 and 6,632,889; and in U.S. patent applications having Publication Nos. 2003/064050 and 2003/023968.
Bone metastases are one of the most common complications related to advanced malignancies, particularly in the three leading cancers; breast cancer, prostate cancer and lung cancer. Bone metastases from breast cancer are typically osteolytic, involving the mobilization of osteoclasts that cause pathological bone resorption, with intense pain, bone fractures, nerve compression, and hypercalcemia. The development and osteolytic nature of these lesions are based on complex interactions between cancer cells and bone marrow stroma in a cycle of bone destruction and tumor expansion. The complexity of cellular interactions and molecular components implicated in bone metastasis has hindered a mechanistic elucidation of key biological features of this process, in particular the basis for long-term survival of metastatic cells in the bone marrow.
Chemotherapeutic agents, hormonal deprivation and bisphosphonates are the common treatments for advanced metastatic disease. However, with time, the disease progresses to a phase when the standard therapy fails to control the malignancy and further progresses to a highly chemotherapy-resistant state.